1. Field of the Disclosure
The technology of the disclosure relates to optical attenuation of light communicated to and/or from an optical fiber.
2. Technical Background
Optical fibers can be used to transmit or process light in a variety of applications. Examples include delivering light to and receiving light from integrated optical components or devices formed on substrates, and transmitting information channels in wavelength-division multiplexed optical communication devices and systems. Other examples include forming fiber optic switch matrix devices or fiber array to array connectors, and producing optical gain for optical amplification or laser oscillation. Optical fibers essentially operate as “light pipes” to confine light within the optical fiber boundary and transfer light from one point to another.
A typical optical fiber may be simplified as having an optical fiber core and a cladding layer surrounding the optical fiber core. The refractive index of the optical fiber core is higher than that of the cladding to confine light. Light rays coupled into the optical fiber core within a maximum angle with respect to the longitudinal optical fiber axis of the optical fiber core are totally internally reflected at the interface of the optical fiber core and the cladding. Total internal reflection (TIR) is an optical phenomenon that occurs when a ray of light strikes a medium boundary at an angle larger than the critical angle with respect to the normal to the surface. If the refractive index of the material on the other side of the boundary is lower, no light can pass through and all of the light is reflected. The critical angle is the angle of incidence above which TIR occurs. This TIR spatially confines the optical energy of the light rays in one or more selected optical fiber modes to guide the optical energy along the optical fiber core.
The optical power level of an optical fiber link is a function of the optical power level of an optical light source. The optical power level of the optical light source may need to be greater than a predefined minimum optical power level to minimize detection error due to optical detector noise. However, in many optical fiber links, the optical power level must be controlled to not exceed a predefined maximum optical power level such as to meet eye safety requirements or to avoid optical detector saturation. Thus, the optical power level may be controlled to be between a minimum optical power level to minimize detection error and a maximum optical power level for eye safety. However, limiting the maximum optical power level to a predefined maximum optical power level, such as to meet eye safety requirements for example, may limit performance of an optical fiber link. Vertical Cavity Surface Emitting Lasers (VCSELs) for example, operate most efficiently at particular levels of optical power. Departures from this optimal power can reduce efficiency, speed or reliability.